1. Field of the Invention
The present invention relates to a method of manufacturing a cylindrical member having anti-slip projections formed on the axial end faces thereof, and to a method of manufacturing a vibration damping rubber bushing employing the cylindrical member.
2. Description of the Related Art
Cylindrical members have been widely used as structural members by themselves, as well as for components such as inner cylindrical members in vibration damping rubber bushings. One known design of such a cylindrical member is provided on its axial end faces with a plurality of anti-slip projections extending in the diametrical direction, formed in a spokewise pattern overall in the circumferential direction with the object of positioning the fitting and preventing it from rotating with respect to the mounting faces of other components.
Such anti-slip projections are typically produced by subjecting the axial end faces of the cylindrical member to press working by being struck by a punch having a ridged and furrowed pattern on its distal end face, as disclosed in JP-A 5-237582 and JP-A 2004-230740.
However, where anti-slip projections have been formed on the axial end faces of a cylindrical member, when the cylindrical member is installed with its axial end faces pushed against the mounting faces of a component of a vibration-damped linkage, gaps tend to form between the axial end face of the cylindrical member and the opposed face of the other component between adjacent anti-slip projections. A resultant risk is that rainwater can seep through these gaps and penetrate to the inner circumferential face of the cylindrical member, causing problems such as rust or corrosion.
In order to address this problem of penetration by rainwater it could be contemplated to redesign the shape of the anti-slip projections that are produced on the axial end faces of the cylindrical member, but a problem is that conventional press working processes of the sort discussed above were limited in terms of the pattern of projections that could be produced. Thus, it was not possible to avoid using anti-slip projections of conventional construction extending in a spokewise pattern overall in the diametrical direction, which made it exceedingly difficult to solve the issue of penetration by rainwater through modification of the shape and pattern of the projections.